Spider Iii (3) 75watt Guitar Amp, Cd-in Feedback Broken?

I've had my spider III, 75watt for a few years now. It's been fine apart from the plastic nut that holds the MP3 line in comes off regularly. however I've made sure it's been locked in fine recently.

However after what I can assume to be a power cut a couple of weeks ago, the MP3-in/ Line-in, instead of playing the input aloud it simply sends out a full volume buzzing feedback noise as soon as the jack is in.

It doesn't matter if the volume on the input is mute or if the guitar jack is in also, when in only guitar mode it amps it the guitar fine, full range treble to bass.

I'm thinking there may be a separate fuse for the MP3-in line, which has now blown maybe?

Just wondering if anyone else has had this problem and managed to sort it, i'm thinking it's gunna be a take apart job?